path: root/users/wpcarro/scratch/simple-select/main.py

import string
from scanner import Scanner
from parser import Parser

################################################################################
# Predicates
################################################################################

def is_alpha(c):
  return c in string.ascii_letters

def is_digit(c):
  return c in "0123456789"

def is_alphanumeric(c):
  return is_alpha(c) or is_digit(c)

def is_whitespace(c):
  return c in " \r\t\n"

################################################################################
# Tokenizer
################################################################################

AND    = ("CONJUNCTION", "AND")
OR     = ("CONJUNCTION", "OR")
NOT    = ("PUNCTUATION", "NOT")
COLON  = ("PUNCTUATION", "COLON")
LPAREN = ("PUNCTUATION", "LPAREN")
RPAREN = ("PUNCTUATION", "RPAREN")

def tokenize(x):
  s = Scanner(x)
  tokens = scan_tokens(s)
  return tokens

def scan_tokens(s):
  result = []
  while not s.exhausted():
    if is_whitespace(s.peek()):
      s.advance()
    else:
      result.append(scan_token(s))
  return result

def scan_token(s):
  punctuation = {
      "-": NOT,
      ":": COLON,
      "(": LPAREN,
      ")": RPAREN,
  }
  c = s.peek()
  if c in punctuation:
    s.advance()
    return punctuation[c]
  if c == "\"":
    return tokenize_string(s)
  if c == "/":
    return tokenize_regex(s)
  if is_alpha(c):
    return tokenize_identifier(s)

def tokenize_string(s):
  s.advance() # ignore opening 2x-quote
  current = ""
  while s.peek() != "\"" and not s.exhausted():
    current += s.advance()
  if s.exhausted():
    raise Exception("Unterminated string")
  s.advance() # ignore closing 2x-quote
  return ("STRING", current)

def tokenize_regex(s):
  s.advance() # ignore opening forward-slash
  current = ""
  while s.peek() != "/" and not s.exhausted():
    current += s.advance()
  if s.exhausted():
    raise Exception("Unterminated regex")
  s.advance() # ignore closing forward-slash
  return ("REGEX", current)

def tokenize_identifier(s):
  conjunctions = {
      "AND",
      "OR",
  }
  current = s.advance()
  while is_alphanumeric(s.peek()):
    current += s.advance()
  if current.upper() in conjunctions:
    return ("CONJUNCTION", current.upper())
  else:
    return ("IDENTIFIER", current)

################################################################################
# Parser
################################################################################

# EBNF
# Note: we order expression types by ascending levels of precedence.
#
# expression  -> conjunction ;
# conjunction -> selection ( ( "AND" | "OR" )? selection )* ;
# selection   -> "-"? IDENTIFIER ":" ( REGEX | STRING ) | grouping ;
# grouping    -> REGEX | STRING | "(" expression ")" ;

def parse(x):
  tokens = tokenize(x)
  p = Parser(tokens)
  return expression(p)

def expression(p):
  return conjunction(p)

def conjunction(p):
  lhs = selection(p)

  while not p.exhausted() and p.test(lambda tokens, i: tokens[i] not in {LPAREN, RPAREN}):
    conj = p.advance() if p.peek()[0] == "CONJUNCTION" else AND
    rhs = selection(p)
    lhs = ("CONJUNCTION", conj[1], lhs, rhs)

  if not p.exhausted():
    raise Exception("Encountered more tokens than we can parse: \"{}\"".format(p.tokens[p.i:]))

  return lhs

def selection(p):
  negate = False
  if p.peek() == NOT:
    negate = True
    p.advance()

  if p.peek()[0] != "IDENTIFIER":
    return grouping(p)

  ident = p.expect(lambda x: x[0] == "IDENTIFIER")
  colon = p.expect(lambda x: x[1] == "COLON")
  value = p.expect(lambda x: x[0] in {"REGEX", "STRING"})
  return ("SELECTION", negate, ident[1], value)

def grouping(p):
  if p.peek()[0] == "REGEX":
    return p.advance()

  if p.peek()[0] == "STRING":
    return p.advance()

  if p.peek() == LPAREN:
    p.advance()
    expr = expression(p)
    p.expect(lambda x: x == RPAREN)
    return ("GROUPING", expr)

################################################################################
# Main
################################################################################

def main():
  while True:
    x = input("> ")
    print(parse(x))

if __name__ == "__main__":
  main()